Electric products, which are broadly used in daily lives, are configured to be driven based on conduction of a current when the current flows through a control line. For example, a relay is configured to close an electrical circuit when a current flows through a control line included in the relay, and to open the electrical circuit when a current does not flow through the control line. However, if the control line is shorted or open for any reason, the current abnormally flows through the control line and thus a driven load may not be controlled.
A representative example of the above-described relay is a relay used in an electric vehicle. The electric vehicle, which attracts global attention these days, includes a relay to control electrical connection between a secondary battery and an electric motor. The relay is controlled by a control system of the electric vehicle, and the control system autonomously has a diagnostic function to diagnose the state of a relay control line. However, the diagnostic function of the control system is performed by adding a current sensing circuit to determine whether a current flows through the control line, or by additionally using a high-priced device. Currently, transition of a relay control function to a battery management system (BMS) is highly demanded, and thus the BMS is highly required to autonomously diagnose the relay control line. To autonomously diagnose the state of the relay control line by the BMS, a relatively low-priced and compact diagnostic apparatus is needed.